Answer
$45.83 \ kg$
Work Step by Step
In order to find the mass of the rock that you could carry underwater, we must divide the mass that you can carry on land by the decimal of the percent of the density difference between the water and the rock. (This is because the water is much more dense than the air.) Thus, we find:
$ m = \frac{25}{1-\frac{1000}{2200}}= 45.83 \ kg$
